Alarm system for swimming pools



upu- C. C. LIENAU ETAL ALARM SYSTEM FOR SWIMMING POOLS Feb. 26, 1957Filed Sept. 21, 1953 2 Sheets-Sheet l INVENTO Rs: ('4 RA 6'. A IE/VA uga f/ 11 ci/frrriasowfe Feb. 26, 1957 c. c. LIENAU ETAL ALARM SYSTEM FORSWIMMING POOLS 2 Sheets-Sheet 2 Filed Sept. 21, 1953 new ATTORNEYS:

AL SYSTEM FOR SWIMMING POOLS Carl (1. Lienau, East Orange, N. L, andJoseph C. Patterson, Jr., Falls Church, Va.

Application September 21, 1953, Serial No. 381,324

Claims. (Cl. 340-458) This invention relates to warning systems forswimming pools and more particularly to a system for giving a warningsignal when a body remains submerged in a swimming pool for apredetermined period sufficient to raise a question whether a person isin distressed condition.

On a number of occasions persons have been found drowned in swimmingpools even though many other swimmers were in the pool at the same timeand well trained life-guards were on duty. In cases of distress,resulting in a swimmer sinking to near the bottom of a pool promptdetection is necessary in order to provide the greatest chance forremoving the person from the water before drowning occurs. But in thenormal use of a pool undistressed swimmers are passing through variouszones comprising the pool and divers are passing through zones near thedeep end of the pool and close to the bottom of the pool. Also someobjects of lesser size than the body of a child, such for example asbathing caps, water toys, etc. will on occasion sink to the bottom of apool and will have an effect on signals transmitted through the wateralthough of lesser degree than the body of a small child. It istherefore necessary that the alarm system be able to distinguish betweendistressed persons and non-distressed swimmers or other objects and yetgive alarm quickly enough to leave time for efiectively aiding adrowning person.

It is an object of the present invention to provide a system of theabove mentioned kind.

Another object of the invention is to provide a system in which signalactuating means comprise means for measuring the degree of reduction ina signal transmitted through the water, and rejecting disturbances lessthan a critical minimum amount coacting with means for measuring theduration of the disturbance and rejecting disturbances of less than apredetermined minimum duration.

Another object of the invention is to provide method and means by whichsignals from. a unitary source may be passed a plurality of timesthrough water in a pool, and through a plurality of zones within a poolthus providing a watch over a substantial pool area with a' minimum ofequipment.

Other objects of the invention will be in part obvious or in partpointed out hereinafter.

The invention accordingly consists in the features of construction,combinations of elements, arrangements of parts, and in the severalsteps and relation and order of, each of said steps to one or more ofthe others thereof, all as will be pointed out in the followingdescription, and the scope of the application of which will be indicatedin the following claims.

The invention will best be understood if the following description isread in connection with the drawings, in which,

Figure 1 is an end elevational view showing means, partlydiagrammatically, for creating a closed signalling circuit comprising inpart water within the pool;

States Patent Figure 2 is a view similar to Figure 1 but showing amodification of the signalling means and circuit of Figure 1;

Figure 3 is a view similar to Figures 1 and 2 but showing anothermodification of the signalling means and circuit;

Figure 4 is a view similar to Figure 1 but showing in detail theelectrical portion of the closed signalling system illustrated in Figure1; and

Figure 5 is a schematic view showing graphically fluctuations in thesystem disclosed in Figures 1 and 4 resulting in reductions in thewarning signal insufficient in degree or duration to actuate alarm orresponder means, and other reductions in the warning system which aresufficient in degree and duration of time to actuate such alarm means.

The numeral 10 indicates a swimming pool having therein water up to thelevel indicated by the line 12. On one side of the swimming pool at apredetermined level above its bottom a transducer T1 is positioned andon the opposite wall of the swimming pool at substantially the samelevel the transducer T2 is positioned. The transducers areinterconnected in an enclosed energy circuit which includes filter meansF, amplifying means A, an output level control means L and theoscillator means 0. Also interconnected with the output level control Lis a demodulator D and a delay network d which in turn is connectedthrough a relay, as best seen in Figure 4, to a responder R which may beany desired type of signalling device. Electrical energy transmitted totransducer T1 is transformed thereby into sound energy which istransmitted to the opposing transducer T2 substantially along the lineindicated by the numeral 14 in Figure l constituting the maintransmission path. Lines 16 and 18 indicate smaller portions of energytransmitted by transducer T1 in angular directions. It will be seen thatthe energy travelling along line 16 escapes from the surface of the pooland is dissipated while energy travelling along line 13 is reflected atthe surface of the water 12 to the transducer T2. The line 20' indicatesstray energy which may be from any of a variety of possible sources,including energy from transducer T1 reflected from a point above thesurface of the water.

In the embodiment of the invention illustrated in Figure 1 a warningsignal is given only when energy being transmitted along the line 14 isreduced by any cause by more than a predetermined amount for more than apredetermined time interval. The critical amount of reduction in theenergy transmitted along the line 14 is less than the reduction whichwould be caused by the presence of the body of any person including avery small child anywhere along the path between T1 and T2. The minimumtime interval is determined to be more than the ineriTal of a casualvisit to the bottom of the pool by an active and undistressed swimmerand less than a period determined by physiological considerations.

Figure 2 shows a smaller but somewhat modified embodiment of theinvention in which the transducers T1 and T2 are both positioned on thesame side of the pool and energy transmitted into the water fromtransducer T1 is successively reflected at the points 22, 24 and 26before impinging on transducer T2. The remainder of the circuit may beas described in connection with Figure 1. It will be noted thattransducers T1 and T2 are positioned at an angle, to direct and receivesound signals travelling along a zig-zag path, the angle beingpreferably great enough to insure reflection with a minimum ofabsorption in the reflecting surfaces.

In Figure 3 another embodiment of the invention is shown in which onlyone transducer T is employed which serves .both as the energytransmitting and receiving means. In this embodiment of the inventionenergy is transmitted across the pool and is reflected directly back totransducer T. In this embodiment of the invention the oscillator O isconnected .to a circuit including filter means F, amplifier A and'output level control means L from a point 28 just beyond the outputlevel control to a point 30 between transducer T and filter F.

The apparatus represented in the block diagrams in association withFigures 2 and 3 can be employed in association with a plurality oftransmission-reception channels by the expedient of a scanning orperiodic switching device, not shown. This extension to a system ofmultiple closed transmission-reception channels serves the end of theinvention which ,is to maximize the volume of pool surveyed by a givencomplement of apparatus.

In Figure 4 the elements comprising the system are detailed. Any of anumber of diiferent kinds of transducers may be employed including,magnetic, electrostatic diaphragm, crystal or electro-striction, andmagneto-striction. Filter F may be of knownkind and is selected to passelectric wave energies of frequency spectrum characteristic of thetransducer structure. A is a tuned amplifier with provision forrejecting signals of less than a predetermined amplitude. In theembodiment shown the predetermining element is resistance 32 whichadjusts the grid bias voltage. Its function is to reject signal voltageswhich are less than the predetermined minimum required to actuate thesucceeding elements of the system including particularly the demodulatorand responder system. The inductance 34 and the capacitance 36 serveboth as load impedance and for frequency selective purposes analogous tothe filter F.

Connected across the output terminals 38 and 40 of amplifier A is anadjustable potentiometer 42 by which the desired fraction of theavailable output of the amplifier is passed on by leads 44 and 46 toslip ring means 48 of the demodulator D. For convenience in explanationa voltmeter V is shown connected between leads 44 and 46, readings ofwhich, under circumstances described below, are represented by the curveV1. in Figure 5.

The contact ring means 48 is shown mounted on a rotating cam d actuatedby constant speed motor M, and having the projection 52 which, once foreach rotation of the cam, closes the switch 54 controlling the potentialof grid 2 of the gas discharge tube 56 which, together with thecondenser 58, is indicated generally as comprising the oscillator 0.

Tube 56 is of the kind containing an inert gas which is normallynon-conductive but is rendered conductive when the grid 2 is given apositive potential with respect to the cathode k. Closure of the switch54 places a high positive potential on grid 2. The tube 56 is therebyrendered conductive, effectively connecting condenser 53 from groundindicated at 60 to one terminal 62 of condenser 64, the other terminalof which is indicated by the numeral as. The circuit includingtransducer T1 and condensers 64 and 58 in parallel now oscillates at afrequency determined by the structure of the transducer and thecondensers and thus providing signals which are transmitted to waterwithin pool 1%.

The time of transit of the sound signal through the water is muchgreater than the transmission of the signal from transducer Tz to thedemodulator point. The latter interval is negligible. During theinterval beginning with the closure of switch 54 and ending with thearrival of the pulse signal at the output terminals of the demodulatorthe camturns through an angle proportionate to the time of transit ofthe pulse through the water in the pool from T1 to T2. The arrivingpulse fires the glow discharge tube 68. Positioned in operative relationto tube 68 is the photoceil 79 which is energized by radiation from bulb63 when thelatter is lighted. When cell '70 is energized by impinginglight from bulb 68 current flows from a source of energy B+ through theresistance 72 and the photo cell 70 to ground indicated at 74. Thepotential drop developed across the resistor 72 charges the condenser76. This resistor-condenser combination represents one kind of a delaynetwork. The potential across the condenser 76 holds a relay 78 innormally open position. When glow discharge tube 68 is extinguished theVoltage across condenser 76 begins to decay and continues to decay aslong as the tube remains extinguished at a time rate dependent upon theresistance and capacitance of the combination 7276. This time constantdetermines the period of delay in closing the relay 78. When the outputvoltage of the delay network falls to a predetermined critical value thenormallyopen contact 80 closes thereby ctuating a responder R to give aWarning signal.

In Figure 5 curve VL represents the hypothetical readings of thevoltmeter of the level indicator L. In the embodiment of the inventionillustrated in Figure 4 it is desirable to use a voltmeter indicatingroot mean square value. In the system described in Figure 4 the pulsesarrive with a repitition rateof considerable frequency in comparisonwith the period of the voltmeter needle and a voltmeter of the abovementioned kind is desirable to prevent vibration of the voltmeterneedle. The diagram in Figure Sassumes that the system has been inoperation beginning at time zero. It is assumed that the water path isclear of interruption for substantially 40 seconds represented byconstant values for V1,. Under these conditions the glow discharge lamp68 will flash at a position displaced by a constant angle from the zeropoint ofits rotation. This interval is described as all clear. The delaynetwork output voltage is sufficient to hold relay contact 80 open, andaccordingly the responder R is inactive.

Reductions in the intensity of the transmitted signal, as indicated byVI. in Figure 5 are of two kinds-those originated in the waterpath andthose in the electrical system connecting transducers T1 and T2. Afluctuation resulting from a supply line voltage or battery voltagechange is illustrated in Figure 5 beginning at 45 seconds and indicatedgenerally by the numeral 82. If sufficient in magnitude such a variationor a circuit failure in the system will actuate the responder R. Thevariation indicated by numeral 82 is, however, less than the criticalamount and is not suflicient to cause responder R to be actuated. Thevariation indicated by the numeral 84 is, however, great enough toactuate responder R if continued for a sufl'lcient interval of time.Variation 84 is not of suflicient duration to actuate R but whencontinued as is illustrated by the portion 36 of the curve it willresult in actuation of R. Variation 84 represents the effect of a casualinterruption of the sound path by the passage of an active orundistressed swimmer through the field of transmission from T1 to T2, ofless duration than the minimum duration of interruption required foractuating responder R.

The curve of delay network output voltage corresponds with thehypothetical variations in the voltage of the voltage level control L,and thus only a small dip occurs at 88 corresponding with thefluctuation 82; a greater dip occurs at 90 corresponding with thesubstantial but momentary decrease in voltage indicated at 84; but itwill be noted that thedip 92 corresponding with the prolonged decreasein voltage indicated by the numeral 86 extends down below the lineindicating the critical voltage for operating the responder, this linebeing crossed after a-period marked Delay which represents thepredetermined time interval ofiinterruption for actuating the responder.Once the alarm signal is actuated it will continue to actuate until theinterfering body is removed from the field of energy transmissionbetween T1 and T2, which in curve 86 is indicated by the return in thecurve to its normal level at the point marked Recovery. Continuedinterruptionpf the signal transmission would result in continuedactuation of the responder R as indicated by the hatched line on theright hand side of the portion of the curve marked 92.

In Figure 4 the switch s1, s2 is shown provided with a movable contactmember 94 illustrating an alternative manner of triggering the pulsegenerator. When s1 is open and s2 is closed the grid 1 of tube 56 isconnected to the output of the amplifier. The arrival of a pulse at grid1 initiates a second pulse train of oscillations in transducer T1. Asecond pulse train of oscillations is initiated in the manner previouslydescribed and proceeds through the water, transducer T2, filter andamplifier to the glow tube 68. The second pulse upon arrival initiates athird pulse in the same manner through grid 1. During the interval thecondenser 58 has been recharged from the energy source B+ through theresistor 59. Accordingly the train of pulses is self-maintaining. Thesepulses are represented by flashes of the glow discharge tube 68 which wemay now assume is to be stationary. If the water path .be interrupted aspreviously described the train of pulses is diminished in intensity orceases altogether as soon as absorption of energy by the obstruction inthe water path is sufficient. The glow discharge tube is thenextinguished. The glow discharge tube is itself a responder but ispreferably supplemented by the delay network d and responder Rpreviously described.

If tube 56 is a vacuum instead of a gas tube oscillations can beobtained which form a periodic pattern in time which may be described ascontinuous rather than pulse modulated. A pulse signal pattern ispreferred because with it more discriminatory information as to thenature and cause of the reduction of the transmitted signal may beobtained.

By the means described above a delayed action response system isprovided which rejects casual reduction of the transmitted signal andgives a positive alarm desired when a reduction energy of predeterminedminimum intensity has continued for a predetermined minimum duration oftime. By the means disclosed it is possible to make a continuous searchof the pool bottom which due to splashing of the water at its surface,or the low visibility of the water, or to lack of observers, would nototherwise be made. By the means described in Figure 2 a singlesignalling circuit can be employed to search" or keep watch over a poolarea of substantial length and width.

It will thus be seen that there has been provided by this invention amethod and apparatus in which the various objects hereinabove set forthtogether with many thoroughly practical advantages are successfullyachieved. As various possible embodiments might be made of themechanical features of the above invention and as the art hereindescribed might be varied in various parts, all without departing fromthe scope of the invention, it is to be understood that all matterhereinbefore set forth or shown in the accompanying drawings is to beinterpreted as illustrative and not in a limiting sense.

What we claim is:

1. A system for detecting the presence of a body in a pool and giving analarm which comprises, means for transmitting energy through water in apool at a predetermined distance above the bottom of the pool, means forreceiving energy transmitted to said means through water in said pool,alarm means, and means for actuating said alarm means when transmissionof energy from said transmitting means to said receiving means isdiminished more than a predetermined minimum amount for more than apredetermined minimum of time including, a source of energy, means formeasuring the intensity of the energy, and means for measuring the timeinterval during which the energy intensity of the transmitted signal isdiminished.

2. The apparatus claimed in claim 1 including means for collimating theradiated energy and means for directing and reflecting it so as to passthrough a plurality of regions of the water in the pool.

3. The system for detecting the presence of a body 111 a pool and givingan alarm which comprises, means for propagating pulses of energy inwater in the pool, means for receiving the energy after it is passedthrough water in the pool, an alarm device, separate means to actuateit, means for utilizing said energy to inhibit said separate means, andmeans for causing the alarm inhibiting means to be actuated only afterthe transmission of energy through the water in the pool has beendiminished for more than a predetermined interval.

4. The apparatus claimed in claim 3 in which means are provided causingthe alarm inhibiting means to be actuated only after a criticalreduction of energy transmitted to the alarm inhibiting means iscontinued for a critical period of time.

5. Apparatus for detecting the presence of a body in a pool and givingan alarm which comprises means for propagating energy in water in a poolin groups of ultrasonic pulses, means for receiving the energy after ithas passed through water in the pool, means for converting the receivedenergy into electric energy, an alarm device, separate means foractuating said alarm device comprising an electric circuit, meansactuated by the energy normally transmitted through the said pool tohold said alarm circuit open, the energy required by said last mentionedmeans being critical in amount, said means being actuated only when theenergy transmitted through the pool exceeds a critical amount, and meansfor closing said circuit when the said means acting to keep it open isnot energized.

References Cited in the file of this patent UNITED STATES PATENTS2,071,933 Miessner Feb. 23, l937 2,411,537 Goodale Nov. 26, 19462,655,645 Bagno Oct. 13, 1953 FOREIGN PATENTS 656,399 Great Britain Aug.22, 1951

